1. Field of the Invention
The present invention relates to a surface acoustic wave device used for a resonator, a filter, or other component, and more particularly, the present invention relates to a surface acoustic wave device in which a plurality of insulating films are stacked on an IDT electrode.
2. Description of the Related Art
Hitherto, surface acoustic wave devices have been widely used for resonators, band filters, and the like.
For example, Japanese Unexamined Patent Application Publication No. 7-254835 described below discloses a surface acoustic wave resonator filter shown in FIG. 14. A surface acoustic wave resonator filter 1001 includes an X-cut LiTaO3 substrate 1002. An electrode structure including IDT electrodes 1003 and 1004 and reflectors 1005 and 1006 is disposed on the X-cut LiTaO3 substrate 1002. A SiO2 film 1007 is disposed so as to cover the electrode structure.
In this device, a response of the fundamental mode of a surface acoustic wave is used and the thickness H of the SiO2 film 1007 is set in the range represented by the formula: 5%<H/λ<15%, where λ is the wavelength of a surface acoustic wave. It is described that, thereby, the frequency-temperature characteristic can be improved, and the electromechanical coupling coefficient can be increased.
In recent years, electronic devices utilizing higher frequencies have been increasingly used. In the surface acoustic wave resonator filter 1001, in order to allow higher frequencies to be used, it is necessary to narrow the electrode finger pitch of the IDT electrodes 1003 and 1004. However, narrowing of the electrode finger pitch may result in difficulty in processing the IDTs 1003 and 1004, and the yield may be decreased. Furthermore, there is also a problem that the impulse withstand voltage may be decreased, resulting in decreased reliability.